The present invention relates to burner method and apparatus wherein fuels such as gas must have a stoichiometric air/fuel mixture for purposes of combustion to achieve the most efficient flame characteristics.
In conventional propane gas torches, for example, the burner nozzle has a chamber for mixing stoichiometric ratio to achieve a blue flame which has a point of highest temperature to be the most efficient use of fuel. Heating of an object having a large surface area requires passing the torch flame tip back and forth over the area or using a diffusing nozzle to heat it somewhat uniformly.
According to the present invention, a fluidic oscillator incorporated in the burner nozzle sweeps the jet of fuel, which may be somewhat internally mixed with air inside the mixing chamber but most or all of the mixing with air is achieved outside of and downstream of the nozzle and within a predetermined distance. The swept jet fuel mixes with air in the space between the outlet opening so that upon combustion it produces a flame front having an area and thickness determined by the sweep angle and wave pattern of the fluidic oscillator and the rate of mixing proportional to frequency of oscillation is self-regulating to achieve a proper fuel-air ratio needed for combustion. A wide variety of fluidic oscillators are known and useful in practicing of the invention.
Advantages of the invention are that the shape of the hot flame front is expanded and spaced from the physical burner nozzle to achieve a high heat transfer efficiency while at the same time, the physical nozzle remains cool and thus in some applications can be made of plastic. Moreover, by providing oscillators with different frequency of oscillation, and wave patterns, the distance of the flame front and the shape thereof can be adjusted to accommodate different use services or applications.
Almost any fluidic oscillator in which the fuel can be formed into an oscillatable or sweepable jet e.g., a jet that is oscillatable that is sufficient to achieve proper mixing of fuel to be combustible a predetermined distance from the nozzle can be used. Such devices are shown in U.S. Pat. No. 4,052,002 for controlled fluid dispersal techniques, Bray U.S. Pat. Nos. 4,463,904 and 4,645,126, Stouffer U.S. Pat. No. 4,508,267 and Stouffer and Bauer U.S. Pat. No. Re. 33,158 are useful. In the preferred embodiment, it is desired to achieve as much external mixing of the fuel with air as is possible to have as large a detached flame front as possible. In some cases however, fluidic oscillators having diverging outlets sweep the fuel jet back and forth and entrain some air into the nozzle and hence these are likewise useful but do not have as large a spacing between the flame front and the nozzle because there is less efficient external mixing of fuel with air to achieve the stoichiometric ratio.